A method of reconstructing an image that may include in at least one example: determining coincidence events based on detection by a detector during a continuous incremental scanning; determining an axial position for each of the coincidence events; storing data for each of the coincidence events including the axial position in a list mode; sorting the data for each of the coincidence events according to a spatial order; and obtaining an image by performing iterative reconstruction with the sorted data for each of the coincidence events.